Extrusion equipment can be used for producing articles including films, tubes, sheets, foams, parisons, injected molded items and other articles comprising one or more thermoplastic resins. Extrusion dies have been used to form a variety of articles by feeding, melting and conveying thermoplastic resins through flow channels that split the polymeric melt into finer polymer streams that may then be introduced onto one or more feed segments. Feed segments generally comprise a surface on which the individual stream melts may be distributed and recombined to form a melt having a desired thickness and shape. The melt flow may then travel towards a discharge outlet where it can be extruded into a film or shaped article. An ending gap, located in the vicinity of the discharge outlet, controls the emerging thickness of the resulting product wall. In some instances, a feed portion supplying polymer to the die can contain more than one modular feed segment.
In some instances, extrusion assemblies produce an annular film or sheet. In some annular arrangements, disks or frusta can be arranged one on top of another, in a type of “pancake stack” or “stacked platter” fashion. In such cases, one or more feed segments direct molten resin toward a common annular channel where separate streams of molten polymer combine and exit the die through a discharge outlet. After exiting the die, the combined polymer streams are cooled to form articles such as multilayered films or multi-colored articles.
Extrusion dies, especially co-extrusion dies, have generally gained wide acceptance. However, they still have disadvantages and limitations. One common disadvantage of extrusion dies relates to non-homogeneous delivery and/or distribution of molten resin and blends within feed segments. Such non-homogeneities can result in weaknesses or noticeable blemishes within extruded articles, for instance film products.
Thus, there still exists the need for extrusion dies that can process fluids such as molten thermoplastic resins while controlling the homogeneity of fluid blends and/or combined streams.